(a) Field of the Invention
The present invention relates to an electrophoresis apparatus used for analyzing polymers, such as DNA, RNA and proteins, particularly, an electrophoresis member used in DNA sequencers, and to its production.
(b) Description of the Related Art
According to one technique of DNA sequencing, a liquid containing DNA fragments is separated by electrophoresis to detect the fluorescence of each DNA fragment. A conventional method is a slab gel electrophoresis method wherein electrophoresis is conducted in a gel filled between glass plates. Decreased gel thickness and higher voltage are necessary to speed up the electrophoresis separation, but generation of heat has limited the applicable voltage.
A new technique is a capillary electrophoresis method using quartz capillaries of about 10 to 100 μm in inside diameter. Because capillaries decrease the generation of heat, higher voltage can be applied as compared with the slab gel electrophoresis method, increasing the separation speed more than 10 times. At present full automatic multi-capillary system using a capillary array of from several to 100-capillaries-alignment is employed actively.
The multi-capillary array system needs special designs to irradiate a plurality of capillaries with light for exciting fluorescence. There have been developed various systems including beam scanning system, beam spreading system and multi-light source system, which however involve the problems of low irradiation efficiency, low analyzing sensitivity and high cost for a plurality of light sources. A solution disclosed in Japanese Patent Application Non-examined Publication No. H09-96623 (1997) is irradiating light perpendicularly to the capillaries, on a plane wherein a plurality of capillaries are aligned, to irradiate all capillaries with one beam using the lens effects of the capillaries. This system, called multiple focusing system, enables highly sensitive analysis with only one light source.
Another method recently attracting attentions is the chip capillary electrophoresis method disclosed in the specification of U.S. Pat. No. 5,958,694, whereby electrophoresis is conducted through channels (capillaries) of about 10 μm wide and deep made on a surface of a glass or quartz plate by etching or the like. The substrate used is sometimes called an electrophoresis chip. Compared with the conventional capillaries, the electrophoresis chip has the advantage of higher heat releasing effect, enabling production of short, high-density channel arrays. The method, however, is not suit to rapid analysis of a large quantity of sample, because the sample has to be transferred from reaction tubes to the chip by hand labor (pipetting).
Conventionally, capillary arrays have been assembled by bundling capillaries using one assembling jig for every capillary. As the number of capillaries increases, the bundle of capillaries becomes bulky, requiring a large space in an apparatus and making downsizing the apparatus difficult. Further, not only the steps and time of capillary array assembling but also troubles such as the breakage of capillaries are increased. Additionally, in the assembled arrays, most parts of the capillaries are exposed in the air, so that they are easily broken on handling and cannot release heat efficiently due to the air surrounding them. In Japanese Patent Application Unexamined Publication Nos. 2001-264293 and 2001-324475 is disclosed a capillary array wherein the sample injection parts and detection parts of a plurality of capillaries are aligned in parallel by penetrating the capillaries through a box-like load header near the sample injection parts and penetrating the detection parts between two support plates. The most parts of the capillaries of the array are also exposed in the air. Therefore, the capillaries are easily broken on handing and cannot release heat efficiently.